About a third of U.S. teens with diabetes don't know they have the condition, a new study finds. Researchers analyzed information from more than 2,600 adolescents ages 12 to 19 who were tested for diabetes at some point from 2005 to 2014, as part of a national health survey conducted by researchers at the Centers for Disease Control and Prevention. Participants underwent three tests of their blood glucose levels, and a person was considered to have diabetes if at least one test showed the individual had the condition.